Category Archives: moisture management

The bathroom corner issue

Once the Thinset mortar behind the waterproofing membranes has cured, we can start with the preparations for the bathroom floor tiles. We had thought about the tiling for a while already, but more on that in another post.

The plan was to start with the base tiles along the floor and wall edges. That lead us head on to a problem that I really wanted to resolve.

Corners in shower stalls are notoriously difficult to seal and to keep clean. This is where the water usually concentrates and soap residue accumulates. In an attempt to manage the concentration of water in those corners, they are often sealed with a bead of silicone, which in turn appears to be a soap residue magnet.

In short, these corners begin to look skanky really fast.

I am not the only one who has been bothered by this. Somebody else actually came up with a solution that makes the corners more hygenic.

This reversed quarter round or cove shaped profile by Schluter with a 18 mm (almost 3/4 inch) radius is made out of rigid PVC and prevents water from concentrating while being easy to clean. It comes in different depths that correspond to the tile thickness with which it will be used.

The anchoring legs of the profile are set into Thinset mortar. Once cured, the base tiles can be installed. They should end up flush with the cove profile to allow for good drainage.

This is one of these obscure gadgets that add to the longevity of an installation, make for a healthier indoor environment, and help with the moisture management.

To control costs, we only installed the cove profile in the shower stall, where it is most needed and most useful. Let’s see if it will do the job and meet our expectations.


1st floor bathroom waterproofing

The shower drain flashing eased my paranoia about moisture management just a little. It will take a waterproofing membrane to put me more at ease.

We have worked with a waterproofing membrane on the floor and walls in the basement bathroom. That experience is good to have under the belt and should facilitate the work in the 1st floor bathroom.

Dual function

There is more to a waterproofing membrane, or liner, that meets the eye at first. The one obvious benefit is about – yes indeed – moisture management! But there is a second and significant advantage of using a liner. It serves as a isolation membrane.

Think about it this way. The tiles are glued to the concrete floor. If there is some movement in the concrete floor, it will develop cracks. These may be minute cracks – hairline cracks. Still, they would propagate all the way to the tile surface.

Because these cracks keep constantly moving, replacing the cracked tiles is really no solution. The new tiles will just keep cracking too.

The liner or waterproofing membrane, which is flexible in nature, will prevent small cracks from propagating from the concrete floor to the tiles, thus the term isolation membrane.

Prioritizing the functions

The concrete floor in the basement bathroom sits on rigid insulation and a sturdy gravel base. It has a very low potential for cracking. The priority there was on the waterproofing function of a liner. The isolation effect was a welcome added benefit. That allowed us to use the relatively thin Kerdi liner by Schluter that was easy to handle.

The concrete floor in the 1st floor bathroom is a very different beast. It sits in between and on top of floor joists. These will expand and contract depending on the temperature and humidity. Plus they react with some level of deflection to the load that is put on them.

Now picture the concrete floor in this assembly. This has high crack potential written over it. The priority here is to isolating the tiles from the floor, with the waterproofing as the added benefit. For this case we opted for the heavy duty 0.8 mm NobelSeal TS membrane.

Liner installation

As with the floor drain flashing, we again use beads of rubber sealant (NobelSealant 150) to waterproof at the overlap of the liner and around the floor drains. We also got nifty corner pieces that we sealed in place with the same product.

Because the walls of the bathroom have a low potential for cracks to develop, we switched back to a lighter gauge membrane, the Noble WallSeal. We place the membrane on the those walls that are exposed to water–behind the lavatory and the toilet, and of course in the shower stall.

Now we are almost ready for the tiles and a handy gadget that goes along with them. More of that in the next post.


Durability and shower drain flashing

Just in case you haven’t figured this out yet, I am paranoid about moisture and water damage in the building.

And I think I have good reason to be, considering what I encountered during the deconstruction process.

Water damage can cause serious durability issues, and durability is one of those underrated principles when it comes to green building practices, even though it is so simple: The longer we can make things last, the less resources they require over time, and the more sustainable they are.

LEED for Homes embraces the durability principle with the inclusion of a “Durability Management Process” in their check list. It gets a little dry, but only for one paragraph!

The process consists of “Durability Planning,” identifying and listing the various durability risk factors, and, “Durability Management,” a quality control for the installed strategies that lower or eliminate durability risks. A third party verification should assure that everything is kosher, and if so, one may earn up to three LEED points.

What did you say? Bureaucratic? Come on, they have to make some money somehow! And only three LEED points, max? Don’t get me started on the points!

For us, as the property owners, occupants, and contractor on this project, durability with or without paperwork, with or without points, is a no-brainer, because it directly affects our short- and long-term bottom line.

Interestingly enough, the durability issues tabulated in the LEED for Homes guidelines are all about moisture control measures (and as I would argue, plain common sense):

  • Tub, showers, and spa areas – Use non paper-faced backer board on walls.
  • Kitchen, bathroom, laundry rooms, and spa areas – Use water-resistant flooring; do not install carpet.
  • Entryway (within 3 feet of exterior door) – Use water-resistant flooring; do not install carpet.
  • Tank water heater in or over living space – Install drain and drain pan.
  • Clothes washer in or over living space – Install drain and drain pan, or install accessible single throw supply valve.
  • Conventional clothes dryer – Exhaust directly to outdoors.
  • Condensing clothes dryer – Install drain and drain pan.
Source: Leed for Homes Rating System (January 2008), ID-2, Table 1, USGBC

What a nice segway back to my paranoia and our shower drain!

Unlike the basement bathroom, the 1st floor bathroom is located above a living space. The floor construction of that bathroom has wooden floor joists that could begin to rot if they get wet (see also images above).

The drain of our walk in/barrier free shower is the most likely point where water could get into the floor assembly and leak into the basement living space. We will waterproof most of the bathroom (stay tuned for the next post), but the drain warrants one additional step, a drain flashing, to further reduce the risk of leakage.

The drain flashing is formed and shaped to perfectly fit onto a floor drain assembly. No awkward folds or stretching, unlike trying to do the job just with the waterproofing membrane.

The drain flashing (NobleFlex Drain Flashing) is sandwiched between the drain base and drain clamping ring. Two beads of rubber sealant (NobleSealant 150) on the drain base prevent water from escaping under the flashing.

Last but not least, I can screw that drain strainer back into the clamping ring and adjust it to the right height, so that I have positive slope to the drain from the entire shower area.

The next step is the waterproofing membrane (NobleSeal TS), which will overlap with the flashing (see drawing above) and is again sealed with two beads of the rubber sealant. More on that in the next post.


Bathroom cement board

It’s time to put up some walls in the bathroom – which puts me squarely back on one of my favorite building topics: moisture management and indoor air quality (IAQ).

A bathroom, in building science terms, is considered a wet room. Splashes, drips and leaks are inevitable, and can over time lead to structural problems, but also IAQ issues such as mold with negative health impacts on the occupants.

This and any associated durability issues are easy to avoid by falling back onto a few simple moisture management strategies.

One of them is to employ floor drains. We documented the installation of the 1st and 2nd floor bathroom drains in a previous post, and there is more to come in one of the next posts.

Another strategy is to use cement board or fiber cement board as a wall cover in shower stalls, bathtub enclosures, and behind lavatories and toilets.

To give you an idea how water resistant cement board is… I had a leftover piece sitting in the yard for one and a half years, exposed to the elements. It was still in perfectly good shape and I ended up using it for one of our window sills in the basement.

Do not use green board or any other kind of paper-faced gypsum board product. These things are not suitable tile backer products and can turn into big mold traps.

See also Building Science Corporation, Info-306: Interior Water Management

What about the areas that don’t receive tiles, such as the ceiling and the upper half of the wall behind the lavatory and toilet?

Regular drywall will do the job, at the cost of around $6.00 per sheet. The green board products run twice as much (around $12.00 per sheet).

But what about the green board’s mold resistant property? Wouldn’t it prevent mold formation on the walls and in corners? Isn’t that worth the extra cost?

I would say no. Because if a bathroom requires such mold resistant product, there is an insulation/condensation and ventilation issue. And the extra $6.00 per sheet for green board won’t solve those problems, just prolong the denial about the real issues for a little longer.



No one wants to maintain anything these days. I still get requests for maintenance free landscapes. I wonder when we’ll begin to demand windows that don’t require cleaning or trash that carries itself to the curbside for pickup.

That said, getting in the habit of some simple maintenance tasks can make such a big difference, and in many cases save energy.

Yep, this squeegee helps us to save energy! We possibly won’t get rich over it, but I am a fan of the cumulative benefit.

How? I bragged about our new shower curtain and effective ventilation system in the last post. Rather than turning the ERV into the moisture management workhorse, we use the squeegee to lift the heavy weight.

After each shower, we quickly squeegee off the walls and floor in the shower area. That removes a lot of water that otherwise would need to evaporate and get removed by the ventilation system.

By squeegee-ing that water down into the shower drain, we get away with running the ERV on booster mode for 20 minutes instead of an hour. That’s where it saves us energy.

If you do not have a bathroom fan or a poorly operating one, the squeegee could make a big difference, helping you to manage moisture levels and improving your indoor air quality.